1. Field of the Invention
The present invention relates broadly to electro-photographic apparatus utilizing a multicomponent developer and more particularly to means for automatically controlling the concentration of the components of the developer during operation of the apparatus.
2. Background of the Invention
Many prior art devices and apparatus have been employed in the past and some are still in use for detecting toner concentration so as to maintain the resulting copy uniform as to density and definition.
In one arrangement a pair of opposing glass plates provided with facing metallized surface is arranged so that toner passes between the plates which are electrically charged. The charge causes the toner to be attracted to the plates. An optical sensor, causes light to pass through the plates, the amount of toner being sensed is proportional to the amount of light received by the sensor-receptor. The sensitivity of this type of device is fairly low, however, and detection is performed on the fly i.e. as the toner is passing between the plates.
Still another apparatus employs "white" carrier beads with an optical sensor. The amount of "white" light reflected to the receptor varies with the amount of toner thereby enbling a determination to be made as to the concentration of the toner in the apparatus.
Each of the known types of toner concentration sensing devices is useful to a more or less limited degree but no single device provides completely adequate and efficient signal output to prevent deterioration of the output copy for one reason or another. Thus, none of the prior art apparatus is capable of performing completely efficiently and adequately to provide copy whose density, definition and clarity remains constant throughout its period of use.